The present invention relates to devices that dispense a plurality of volatile air treatment chemicals by heating at least one substrate impregnated with, or coated with, the chemicals, and that can also include indicators to indicate when the treatment chemical(s) have been used up.
Substrates (particularly porous substrates) have previously been used as carriers for air treatment chemicals such as insect control active ingredients, fragrances and deodorizers. See e.g. U.S. Pat. Nos. 5,111,477; 5,647,052, 6,551,560 and 6,663,838. “Insect control active ingredients” includes insecticides, insect repellants or attractants, insect growth inhibitors, and other materials that affect the behavior or development of insects and other arthropods commonly controlled with insects. The disclosure of these patents, and of all other patents, patent applications, patent application publications, and other documents referred to herein, are incorporated by reference as if fully set forth herein. Upon heating the substrate, a volatile air treatment chemical is caused to be dispensed from the substrate. The heating source is typically an electrical heater, but may instead employ combustion of a fuel.
With sufficient use the chemicals are eventually depleted. This depletion time frame is typically much shorter for the chemicals than the useful life of the rest of the device, particularly the electrical heating element and associated housing and electrical connector. Consequently, there has been designed a variety of devices that allow for a chemical reservoir refill unit to be replaced. See generally U.S. patent application Ser. No. 11/346,697 filed Feb. 3, 2006; Ser. No. 11/359,090 filed Feb. 22, 2006; and Ser. No. 11/379,495 filed Apr. 20, 2006. The disclosure of these applications are incorporated by reference as if fully set forth herein. Such devices permit replacement of a subassembly that holds the chemical to be dispensed to the air, and/or a use-up cue indicator, thereby eliminating the need to replace the heating subassembly.
Such devices have significantly advanced the art. However, they are primarily designed for situations where a single air treatment chemical is dispensed from one dispenser, and a use-up cue chemical is volatized from another. For example, a desirable insecticide or insect repellent may not have an optimal fragrance. Hence, it may be desirable to simultaneously mask or improve the smell of the insecticide by also delivering a fragrance to the air. However, the structure for controlling delivery of the primary insecticide may not be optimized for desirable fragrances, and mixing the fragrance with the use-up cue for dispensing therewith may complicate the coordination of the use-up cue chemical with use of the primary active.
Thus, a need exists for improved air treatment devices where a second chemical (apart from the primary active and the use-up cue) can be dispensed in a more efficient manner.